nip54: improve normalization and add tests.

nip54/nip54.go

@@ -1,17 +1,26 @@
 package nip54
 
 import (
-	"regexp"
 	"strings"
+	"unicode"
 
 	"golang.org/x/text/transform"
 	"golang.org/x/text/unicode/norm"
 )
 
-var nonLetter = regexp.MustCompile(`\W`)
-
 func NormalizeIdentifier(name string) string {
+	name = strings.ToLower(name)
 	res, _, _ := transform.Bytes(norm.NFKC, []byte(name))
-	str := nonLetter.ReplaceAllString(string(res), "-")
-	return strings.ToLower(str)
+	runes := []rune(string(res))
+
+	b := make([]rune, len(runes))
+	for i, letter := range runes {
+		if unicode.IsLetter(letter) {
+			b[i] = letter
+		} else {
+			b[i] = '-'
+		}
+	}
+
+	return string(b)
 }